Crowson (U.S. Pat. No. 3,605,888) considers a method for secondary recovery of oil in which electrical current is caused to flow through water in the bottom of a bore hole to produce heating of the water. In one embodiment the water is contained within a reservoir until the temperature of the water is sufficiently high to produce steam at the pressure present in the oil-bearing strata. The water and steam are then released from the reservoir into the strata.
Hendrick (U.S. Pat. No. 3,954,140) contemplates having heating elements at different bore hole levels to heat adjacent hydrocarbon-containing formations to a predetermined level in excess of about 600.degree. F., e.g., about 575.degree. to 725.degree. F. for a typical oil shale formation, thus producing hot hydrocarbon gases which are driven from the heated portions of the formation and passed through porous casing before being drawn through a suction line to a fractionator. Thereafter, temperature in lower bore hole levels is increased to a higher temperature, e.g. about 1200.degree. F. for a typical oil-shale formation, and the process is continued until each higher bore hole level is heated to the higher temperature.
Carpenter (U.S. Pat. No. 4,037,655) connects a plurality of electrodes in contact with salt water and oil in a subterranean formation to a source of electrical power for establishing an AC electrical field of current flow between the spaced electrodes. The AC electrical current path through the formation generates volumes of free hydrocarbon in the formation where it is trapped for increasing the formation pressure. The increased pressure of the formation drives the oil into producing bore holes spaced from the electrode bore holes. Carpenter (paragraph bridging columns 1 and 2) cites prior-art patents related to introducing electrical current into a subsurface oil- or mineral-bearing formation for the express purpose of heating the formation in order to lower viscosity and stimulate flow of oil or minerals in the immediate area involved in the heating process.
Tubin (U.S. Pat. No. 4,127,169) stimulates the flow of oil in the formation traversed by a bore hole to cause migration of the oil into the bore hole where it is recoverable to the surface by conventional techniques. He generates steam in situ within the bore hole from surface-supplied water in heat-transfer proximity to the pay zone of said formation.
He injects thermal energy directly into the pay zone at a preselected depth and at a temperature usually ranging from 250.degree. to 450.degree. F. Cold water is pumped down a string of tubing into a tool where it is converted into steam, and thus-generated steam is forced out into the formation.